Large diameter fiber optics, often referred to as "flexible light pipes", are well known in the art, and typically comprise a single, solid core fiber which is surrounded by a cladding layer and a sheath or shielding layer. The core is the portion of a light pipe which transmits light, and typically has a diameter of about 2 to 12 mm. It is formed of a very soft, semi-liquid plastic material, such as OPTIFLEX.RTM., which is manufactured by Rohm & Haas Corporation, of Philadelphia, Pa. The cladding layer typically comprises polytetrafluoroethylene (PTFE or TEFLON.RTM.), or the like, while the outer sheath is fabricated of a material such as polyvinylchloride (PVC). Unlike small diameter optical fibers, which are typically used to transmit information in relatively complex control systems, these large diameter "light pipes" are typically employed in a variety of illumination systems where direct lighting is difficult to maintain, dangerous, or subject to vandalism. Examples include architectural lighting, display cases, pools and spas (to eliminate electrical connections near water), hazardous material zones (to eliminate the need for sealed lighting), or jail cells. They are particularly advantageous in that only a single centralized illumination system must be maintained, rather than a plurality of individual lights.
There are problems, however, in implementing such light pipe illumination systems because of the difficulty of illuminating a plurality of light pipes from a single illumination source. In order to maximize efficiency, the optical fibers must be bundled as closely as possible, to ensure the maximum ratio of core area (the part of each light pipe which actually transmits light) to total area. However, bundling the large diameter light pipes together in order to illuminate them from the single illumination source is difficult to do efficiently. Each of the individual light pipes are round and thus have a great deal of space between them due to the cladding and shielding layers. This problem is illustrated in prior art FIG. 1, wherein a bundle 2 of large diameter optical fibers or light pipes 4 is shown. Each optical fiber 4 comprises a core 6, a cladding layer 7, and a shielding layer or sheath 8, as described above. To obtain maximum efficiency, it is desirable to illuminate only the core 6 of each of the bundled optical fibers 4. Necessarily, if the light from the source of illumination is spread across the array of optical fibers, it will illuminate not only the cores 6 of the optical fibers 4, but also the cladding layers 7 and the shielding layers 8.
Furthermore, the voids 9 between the optical fibers, which are inevitable because of the fibers' round dimensions, also are impacted by the light from the illumination source. All of the light falling upon any element other than the cores 6 is wasted, and becomes an efficiency loss, since it will not be transmitted by the fibers. Additionally, packing the fibers so closely together creates problems such as mechanical difficulties in configuring and accommodating the illumination system and difficulties encountered in attempting to replace one of the individual bundled fibers. This design also typically results in color variation between fibers unless techniques are specifically employed to prevent this problem.
One prior art solution, variations of which have been disclosed in parent application U.S. Ser. No. 08/374,163, now U.S. Pat. No. 5,559,911, U.S. Pat. No. 5,396,571 to Saadatmanesh et al., and U.S. Pat. No. 5,222,793 to Davenport et al., for example, is to illuminate only the core of each output fiber, rather than illuminating the entire optical fiber bundle. Such an approach is advantageous, for example, because by preventing the incidence of light on other optical fiber elements, such as the shielding or cladding layers, as well as voids between fibers, the efficiency and light output of the illumination system is greatly increased. Also, because the whole image of the arc of the lamp is received by each individual fiber, rather than collectively on a bundle of fibers so that each fiber receives a different part of the arc, color variation between fibers is eliminated. Furthermore, using such a concept, it is possible to space the optical fibers, rather than bundling them, which multiplies their versatility in various applications.
One disadvantage of these recent systems, however, is their use of illumination reflectors to transmit light between the source of illumination and the output optical fibers which are based upon classic conic sections; i.e. elliptical or parabolic reflectors. Such reflectors are best for "ideal" light sources; i.e. "point" sources, but for "real world" light sources, light transmission efficiency is reduced.